From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AA45C43381 for ; Mon, 18 Feb 2019 08:07:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4A4C218C3 for ; Mon, 18 Feb 2019 08:07:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729078AbfBRIHb (ORCPT ); Mon, 18 Feb 2019 03:07:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52972 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729034AbfBRIHb (ORCPT ); Mon, 18 Feb 2019 03:07:31 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6911259458; Mon, 18 Feb 2019 08:07:30 +0000 (UTC) Received: from localhost (ovpn-12-45.pek2.redhat.com [10.72.12.45]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B24355F9C0; Mon, 18 Feb 2019 08:07:29 +0000 (UTC) Date: Mon, 18 Feb 2019 16:07:27 +0800 From: Baoquan He To: Kees Cook , "Kirill A. Shutemov" Cc: LKML , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Dave Hansen , Andy Lutomirski , Peter Zijlstra , X86 ML , Mike Travis , Thomas Garnier , Andrew Morton , Masahiro Yamada Subject: Re: [PATCH v3 3/6] mm: Add build time sanity check for struct page size Message-ID: <20190218080727.GH14858@MiWiFi-R3L-srv> References: <20190216140008.28671-1-bhe@redhat.com> <20190216140008.28671-4-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 18 Feb 2019 08:07:30 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/17/19 at 08:50am, Kees Cook wrote: > On Sat, Feb 16, 2019 at 6:02 AM Baoquan He wrote: > > > > Size of struct page might be larger than 64 bytes if debug options > > enabled, or fields added for debugging intentionally. Yet an upper > > limit need be added at build time to trigger an alert in case the > > size is too big to boot up system, warning people to check if it's > > be done on purpose in advance. > > > > Here 1/4 of PAGE_SIZE is chosen since system must have been insane > > with this value. For those systems with PAGE_SIZE larger than 4KB, > > 1KB is simply taken. > > > > Signed-off-by: Baoquan He > > --- > > mm/page_alloc.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 35fdde041f5c..eb6c8e22333b 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -67,6 +67,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -7084,6 +7085,7 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn) > > unsigned long start_pfn, end_pfn; > > int i, nid; > > > > + BUILD_BUG_ON(sizeof(struct page) > min_t(size_t, SZ_1K, PAGE_SIZE)); > > Are there systems with PAGE_SIZE < 1K? Maybe this should just be a > direct SZ_1K check? This check was suggested by Kirill, I forgot adding his "Suggested-by", sorry abou that. Originally he suggested to add code in generic place like this: BUILD_BUG_ON(sizeof(struct page) < min(SZ_1K, PAGE_SIZE/4)); In later post, the kbuild test robot reported an build error on i386 ARCH, http://lkml.kernel.org/r/20180911074733.GX1740@192.168.1.3 >From the report hint, I thought 'PAGE_SIZE/4' also related to the macro expansion, so change it as min_t(size_t, SZ_1K, PAGE_SIZE). Just now I tried the build again, changing it back to 'PAGE_SIZE/4' also works. BUILD_BUG_ON(sizeof(struct page) > min_t(size_t, SZ_1K, PAGE_SIZE/4)); I guess Kirill wants to make it as self explanatory for this check by suggesting it as min(SZ_1K, PAGE_SIZE/4), to stress the 'PAGE_SIZE/4'. As he said in mail thread, "If struct page is more than 1/4 of PAGE_SIZE something is horribly broken". lkml.kernel.org/r/20180903102642.rmzawwqsqjvh2mkb@kshutemo-mobl1 Just try to give more details about this adding, not defend. I am fine to take any of them. > (Also, perhaps this should use the new static_assert where struct page > is defined?) I searched with 'git grep', didn't find static_assert macro or function. And also no finding in include/linux/mm_types.h. Could you please be more specific? Thanks Baoquan > > > /* Record where the zone boundaries are */ > > memset(arch_zone_lowest_possible_pfn, 0, > > sizeof(arch_zone_lowest_possible_pfn)); > > -- > > 2.17.2 > > > > > -- > Kees Cook